Charge Separation Dynamics in CdSe/CdS Core/Shell Nanoplatelets Addressed by Coherent Electron Spin Precession

Area of Science:

• Materials Science
• Quantum Mechanics
• Nanotechnology

Background:

• Colloidal nanostructures like CdSe/CdS core/shell nanoplatelets exhibit unique photophysical properties.
• Understanding carrier dynamics, including surface trapping, is crucial for their optoelectronic applications.

Purpose of the Study:

• To investigate the dynamics of charge separation driven by carrier surface trapping in CdSe/CdS core/shell nanoplatelets.
• To differentiate and characterize the timescales and lifetimes associated with electron and hole trapping and subsequent charge separation.

Main Methods:

• Utilized a three-laser-beam pump-orientation-probe technique.
• Detected electron spin coherence at room temperature.
• Analyzed signals based on Larmor precession frequencies, pump power, and shell thickness.

Main Results:

• Observed two distinct Larmor precession frequencies indicating different dynamical behaviors.
• Electron trapping occurs on a ~10 ns timescale, leading to charge separation with microsecond lifetimes.
• Hole trapping occurs on sub-picosecond to picosecond timescales, resulting in nanosecond charge separation lifetimes.
• Increasing CdS shell thickness suppressed hole trapping but not electron trapping.

Conclusions:

• The study elucidates distinct pathways for electron and hole trapping and charge separation in CdSe/CdS nanoplatelets.
• Findings highlight the significant influence of shell thickness on carrier dynamics.
• Results provide critical insights into the photophysics of nanoplatelets and related colloidal nanostructures.